1. Field of the Invention
The invention relates to an electricity storage device in which an enclosed container contains an electricity storage unit and a coolant for cooling the electricity storage unit.
2. Description of the Related Art
Electrically-powered vehicles, such as electric vehicles and hybrid vehicles, have been actively developed. The demand for secondary batteries, for use as driving or auxiliary power sources for such electrically powered vehicles, that are excellent in performance, reliability and safety is developing.
In the field of electrically powered vehicles, driving or auxiliary power sources are required to have a high power density. As an example of such power sources, there is an electricity storage device that has an enclosed container that contains a battery pack, in which a plurality of cells are connected in series or in parallel, and a coolant for cooling the battery pack. The enclosed container includes a container body, the upper side of which is open, and a top lid that covers the upper opening of the container body.
In the above electricity storage device, when the battery pack produces heat during charging and discharging, the coolant is heated, and the heat of the coolant is dissipated from the enclosed container into the outside of the electricity storage device. In this way, the temperature rise in the battery pack is controlled.
Japanese Patent Application Publication No. 2006-127921 (JP-A-2006-127921) discloses a power supply device including a plurality of battery modules, a case that contains these battery modules, a cooling mechanism for cooling the battery modules contained in the case with the use of circulated coolant, and a radiator that cools the coolant.
However, if an air space exists between the top lid and the coolant, the rate of heat transfer from the coolant to the container will be reduced, and there is a possibility that the cooling of the battery pack will be insufficient. Therefore, when the coolant is injected into the container, the amount of coolant must be accurately measured in order for the coolant to be in contact with the top lid of the container.
Furthermore, the heated coolant will move upward in the enclosed container, and there is a possibility that the dissipation of heat will be impeded if there is an air space between the top lid and the coolant.
A method can be conceived in which a little less coolant is injected into the container, the top lid is fixed to the container, and then the coolant is added through the coolant inlet formed in the top lid. With this method, however, it is troublesome to inject the coolant after the lid has been fixed, and to close the coolant inlet. Moreover, there is a possibility that the strength of the top lid becomes insufficient when the coolant inlet is formed in the top lid.
On the other hand, a method can be conceived in which the coolant is injected to the upper limit level of the container, and the top lid is then fixed to the container. With this method, however, there is a possibility that, when the lid is fixed, the coolant will leak out of the container, which can cause air to be mixed into the coolant, which can in turn result in insufficient dissipation of heat.